In my few days of using Ice Cream Sandwich, I really do love it. Its a significant improvement in many ways. The most notable, in my opinion, is the greatly increased stability of the 4G signal. I haven't had it drop since moving to ICS. That's worth it alone. If it were the only upgrade, I'd be happy, but there's a lot of great additions.
I like the stock ability to take screen shots. I like the UI, I like the rules (ie night time sleep rule where it goes silent and you can customize certain people to ring through when they call).
I haven't used navigation since I upgraded so I can't comment on that as of yet.
However, I wanted to take a poll to see what things you would change or add in the official release.